In a wireless Internet system, terminals transmit CDMA codes for ranging to a base station, and the base station transmits a ranging response message (hereinafter referred to as “RNG_RSP” message) to the terminals.
In the above ranging procedure, with respect to the CDMA codes that are competitively transmitted from the terminals, the base station broadcasts an RNG_RSP message as a response to the successfully received CDMA code to all of the terminals.
FIG. 1 is a diagram illustrating a CDMA code ranging procedure according to the related art.
As shown in FIG. 1, if a plurality of terminals competitively transmit CDMA codes to an uplink of an n-th frame, a base station receives the CDMA codes and calculates power and timing adjustment values for each of the CDMA codes received without a conflict. When the number of CDMA codes received from the plurality of terminals is n and the n codes are received by the base station without a conflict, the base station broadcasts n RNG_RSP messages as responses for the individual CDMA codes. Each of the terminals receives all of the RNG_RSP messages that are broadcast from the base station, and compares a CDMA code, a frame number, and subchannel and symbol numbers transmitted by each terminal and values included in the RNG_RSP messages, and selects an RNG_RSP message transmitted to each terminal.
FIG. 2 is a diagram illustrating a ranging response message according to the related art.
As shown in FIG. 2, a ranging response message according to the related art includes response information for one CDMA code. That is, with respect to each of the CDMA codes received without a conflict, the base station transmits a ranging response message.
A field of ranging code attributes that are included in the ranging response message includes a CDMA code, a frame number, and subchannel and symbol numbers that are received.
If each terminal receives a ranging response message, each terminal compares information included in the field of ranging code attributes of the ranging response message and information of the CDMA code transmitted by each terminal and determines whether the two pieces of information are matched with each other. If the two pieces of information are matched with each other, each terminal uses the information included in the received ranging response message to adjust uplink transmission parameters, such as transmission power, timing, and frequency offset. Meanwhile, if the information included in the field of the ranging code attributes is not matched with the information of the CDMA code transmitted by each terminal, each terminal ignores the received ranging response message.
Data is exchanged between the base station and the terminals in a form of a packet data unit (PDU). The base station appends a header and cyclic redundancy checking (CRC) to the ranging response message in order to construct a PDU. As shown in FIG. 2, a header of 6 bytes and CRC of 4 bytes are respectively appended to the front and rear of the ranging response message for the CDMA code so as to construct one PDU, and the ranging response message is transmitted in a form of the PDU. At this time, since a capacity of the ranging response message for the CDMA code is a maximum of 26 bytes, a PDU overhead ratio that is needed to transmit the ranging response message is very large at 10/36. This causes a problem in that the waste of downlink wireless resources becomes severe when the number of CDMA codes received for each frame and the number of ranging response messages broadcast from the base station are increased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.